Awesome! You've made my day. I also found some "shadows" of lettering on the side of the hulls that appear to say "Hobie 18 World ......" I can't make out the rest of the words. Do you know what they were?

I figured the lettering out, which was "HOBIE 18 NATIONALS MONTEREY CALIFORNIA". I also found shadows for six trim stripes about 1/2" wide and separated by about 1/4". Hopefully you'll have a picture that clarifies the colors. "Hobie 18" was found at the back of the hulls. I could never see any of these shadows before I buffed the hulls.

OK, what you have is a 1989 Hobie 18 World Championship boat. That was the last time base-model Hobie 18s were supplied by Hobie Cat to an event.

The hulls looked like this:

The hulls were gray. You can see how the hull stripe swooped down and under the hull, similar to the Boomer stripe. There's no stripe on the inside of the hull, so it probably stopped at the boat centerline. The forward end of the stripe terminated at the bow number. The standard "Hobie 18" identification sticker is above the swoop. Above that is the "Hobie Alter Signature Model" sticker.

The "Hobie Alter Signature Model" stickers first appeared on boats in the mid-80's. They were put on boats that had upgrades from the factory, like EPO rudders and Harken blocks. Otherwise, the boats are just the same as any other.

I'll see if I can find a close-up of "Hobie 18" and "Hobie Alter Signature Model" stickers.

What I originally thought you were asking about was the 1989 Hobie 16 Nationals in Chicago, IL. The same splash graphic used on those boats was used for the 1989 Hobie 18 Nationals in Erie, PA. That was the last time Hobie 18s were provided at an event - and they were Formula 18s, not base-model Hobie 18s. Competitors were not happy. Those hulls looked like this:

One of those '89 Formula 18 boats found its way up to Charlevoix, MI from about 2005-2012, and I purchased it early last summer and it's now on Glen Lake. Sails need replacing but the boat itself is in good shape. Looks like it had wings mounted at one point, but those disappeared somewhere along the line.

So if my SX hull graphics look exactly like the one pictured from the nationals event, except mine are yellow and sport a 31 on the bows, is it one of the original nationals boats? I'll have to post pics on here soon.